1. Field of the Invention
The present invention relates to a method for controlling a brake pressure booster utilizing hydraulic brake pressure boosting.
2. Description of Related Art
Hydraulically assisted brake pressure boosters are increasingly used instead of conventional vacuum-based brake pressure boosters. One reason for this is the additional cost of the vacuum supply in modern motor vehicles, because the intake manifold is not available as a vacuum source in diesel vehicles per se, and also an adequate intake manifold vacuum is no longer continuously available in vehicles with spark ignition because of occasional engine shutdown or operation with a wide open choke flap.
In contrast, a supply pump for an electronic stability controller (ESC) can be used as a pressure fluid source in an advantageous manner with hydraulically assisted brake pressure boosters (in general, a pressure reservoir is still necessary in addition). There are synergy effects from such dual use of the ESC pump unit.
Suitable brake pressure boosters are known e.g. from U.S. Pat. No. 4,678,243 A or DE 102011007095 A1, which are to be made the subject matter of this disclosure with respect to the detailed design of the brake pressure booster and the associated control arrangement.
U.S. Pat. No. 8,038,228 B2 uses the brake pressure gradient as a triggering criterion for an additional pressure source. U.S. Patent Publication No. US20110270500 A1 activates the additional pressure source depending on the pressure in the tandem brake master cylinder.
A common comparison test for brake systems of motor vehicles—which however is not part of legally specified tests—is the so-called AMS brake test, which refers to the German automobile magazine “Auto Motor and Sport.” The test consists essentially of maximally accelerating a vehicle laden with the permissible loading ten times in immediate succession from 0 to 100 km/h and then decelerating back by means of full braking with the antilock braking system responding. This test places special requirements on the temperature behavior of the brake system, especially with respect to brake fade.
An AMS brake test of the hydraulic brake pressure assistance in current brake pressure boosters provides little or no benefit. A more detailed analysis shows this is apparently because the additional hydraulic pressure source is activated throughout; but the application points and activation criteria for activating the additional braking assistance with known brake controllers are so unfavorable that at the point in time of activation there is already such a high brake pressure that the common ESC pumps or the non-return valves disposed in the hydraulic path cannot transport any more brake fluid or supply the brake pressure booster.